well if you are talking about stripes to indicate ready for breeding, there are many signs for a betta to show whenr ready to spawn. such as, the betta will do a head down, fins clamped dance, show her stripes, or flare back at the mate.
if you are talking about stripes to indicate happiness or depress, there are also many signs. one sign is the stripes become horizontal which means the betta is depress or not happy, and two the betta's colors will begin to fade away.
if your gf's female betta has a big belly, it shows that she is full of eggs and could be ready to spawn. when bettas are fed alot they get fat and they also grow, their belly doesn't just grow, their fins and the rest of the body also grows too
